Wave length modulator



May 8, 1945. M. G. CROSBY 2,375,527

WAVE LENGTH MODULATOR- Filed ct. 29, 1941 FJ79 Y L D INVENTOR Patented May 8, 1945' v oFFlca WAVE LENGTH MonULA'ron Murray G. Crosby, Riverhead, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application Gctober 29, 1941, vSerial No. 416,941

' 1o claims.

This application concerns a newl and improved wave length modulator of the locked oscillator type wherein two tube systems and their electrodes are connected in oscillationgenerating circuits such that each tube and its circuits considered separately and individually operates at a different distinct frequency, the circuits including common elements whereby the separate -tub'e oscillators are entrained to operate at a single' mean frequency intermediate the separate distinct frequencies. Oscillators of this type have frequency determining or controlling elements, and in myl new and improved system a single crystal is arranged to control or determine the frequency of operation of the tube oscillators considered separately and as entrained. The tube systems are then differentially modulated to modulate their frequency of operation about said ,mean frequency and within said separate frequencies as limits.

In my improved system the single piezo-electric crystal is placed in a holder having three electrodes, one of which is common, so that the circuits of the two tube generators may be caused to operate at the distinct frequencies by adjusting the separate pairs of electrodes fordilerent tube circuits and is connected by a conducting member I2 on the screw I I .to the cathodes K and K'. Crystal I is placed between the electrodes 2,

3, and 4, with electrode 2. being the common grounded electrode and electrodes 3 and 4 being the separateoutput electrodes. The connections between the grids G1 and Giand electrodes 3 and 4, respectively, are made by way of metal collars I3-and I4 on the screws I0 and 9 respectively. The air gaps for electrodes 3y and 4 are adjusted if desired for different values by means of knobs I and 8. Knob 6 adjusts a lower electrode 2 so as to adjust both air gaps at once and thus vary the mean frequency of operation of the entrained generators.

The locked oscillator type of wave length modulator as stated above tends to operate at two different distinct frequencies -so that two separate frequency determining circuits are required which if taken alone allow each separate oscillator to oscillate at different frequencies.v In my arrangement, grid G1 and anode A of tube I5 areA air gaps or by adjustment of external capacities associated with the crystals and their air gaps.

To my knowledge all prior system of this type use tuned circuits or transmission lines for control of the frequency of operation. In my system, as stated above, a single piezo-electric crystal is used for the frequency control element.

In describing my invention, reference will be made to the attached drawing wherein; .Figure 1 illustrates schematically a wave length modulator of the entrained oscillator type arranged in accordance with my invention, while Figure 2 is a modification of the arrangement of Figure l.

In the drawing, tubes I5 and I6 are the separate oscillation generating tubes which are locked in step. The anodes A and A of these tubes arey connected to a tuned circuit I1 common to the plate circuits of both tubes. 'I'he wave length modulation oscillations generated as described more in detail hereinafter may be supplied from tuned circuit I1 to amplifying, frequency multiplying. and transmitting means as. desired. The grids G1 ,and Gi' of the tubes are connected to the electrodes 3 and 4 of the holder for piezo-electric crystal I. This holder isof a special type which allows different air gaps for the electrodes 3 and 4. The crystal holder includes an insulating member 5 in which are mounted screws 9, Ill, and II, upon which are mounted the electrodes 4, 3, and 2 reconnected by piezo-electric crystal I with contacts 2 and 3 in an oscillation generator of the type wherein the anode circuit I1 .is tuned above the operating frequency and thefeed back is between the anode A and grid Gi. This circuitl maybe l considered one of the oscillator circuits. Tuned circuit I1, taken with grid G1 and A' and piezoelectric crystal I and holders 2 and 4, may be considered the other oscillator. Since the crystal holder capacities are relatively detuned, the oscillators tend to operate at different frequencies.

These two frequencies 'of operation are spaced just far enough apart so that when the two oscillators are coupled together they will lock in step and oscillate at one frequency. The common elements in the separate oscillator circuits entrain the two oscillators so that they operatev at a common frequency.

The'grids Gc and Gs are connected differentially to the secondary winding of a transformer I8, the primary winding of which is connected by `lack I9 to a source of modulating potentials. Thus, by modulating the relative amplitude of oscillations of the two oscillation generators the oscillation frequency of the system shifts troni the normal frequency of one oscillator to the normal frequency of the other oscillator.

In accordance with my invention, the frequency of one of the oscillators is tuned to be different from that of the other oscillator by making the air gaps produced by electrodes 3 and 4 different..v It is known that the frequency of oscillation of a spectively. The electrode 2 is common to both 55 Crystal iS dependent upon the air` gap between the s which a three-electrode crystal holder is also used.

Here, however, instead of varying the relative air gaps of the electrodes II3 and |02 and H4 and |02, I vary the capacity of two condensers C and e C' in shunt respectively to the electrodes H3 and |02 and H4 and |02. These condensers C and C" are placed across the crystal outputs and are adjusted for the frequency at which the tube generators,l when considered separately and individually, are to operate. In this modification the separate generators are, as before, entrained to operate ata common frequency. It is'well known that the oscillating frequencies of a crystal may be varied by varying external capacities in this manner.

What is claimed is:

1. In a wave length modulation system, a pair of electron discharge tubes each having oscillation generating electrodes, a piezo-electric crystal hav.

ing three electrodes, connections including two of said crystal electrodes coupling the oscillation generating electrodes of one of said tubes 1n a i regenerative circuit including said crystal as a frequency determining element, connections inlcludng the remaining crystal electrode and one of said two crystal electrodes coupling the oscillation generating electrodes of the other of said.

tubes in a regenerative circuit including said crystal as a frequency determining element. means 1ncluding at least a pair of said crystal electrodes for tuning said crystal to operate at one frequency 'in one regenerative circuit and to operate at a second frequency in the other regenerative circuit, means for differentially modulating said tubes in accordance with signals, and an output circuit coupled to said regenerative circuits.

2.' In a. wave length modulation system, a pair of electron discharge tubes having output electrodes coupled with a common output circuit, said tubes having `input electrodes, a piezo-electric crystal having three electrodes and having means for 'adjusting the distance between at least -two of said electrodes, connections including two of said crystal electrodes coupling the input and output electrodes of one of said tubes in a regenerative circuit including said crystal, connections ini cluding the remaining crystal electrode and yone of'said two of said crystal electrodes coupling the input and output electrodes of the other of said tubes in a regenerative circuit including said crystal, and connections for modulating the impedances of said tubes in phase displaced relation in 'accordance with signals.

another of .said holder electrodes to an electrode Vof one of said devices., connections coupling the third of said holderelectrodes to a corresponding electrode of the other of said devices, and circuit connections for modulating the impedances of said devices in phase displaced relation in acy y cordance with` signals.

4. In a wave length modulation system, a pair of electron discharge tubes each having oscillathe oscillation generating electrodes of the other of said tubes in a regenerative circuit including said crystal as a frequency determining element, capacitive means forftuning said crystal to operate at one frequency in one regenerative circuit and to operate at a second' frequency in the otherv regenerative circuit, means for diierentially modulating-said tubes in accordance with signals, and an output circuit coupled to said regenerative circuits.

5. In a wave length modulator, two electron discharge systems each having oscillation generating electrodes, a piezo-electric crystal having a plurality of electrodes, connections including two of said crystal electrodes connecting the oscillation generating electrodes of one of said systems a regenerative circuit including said crystal as a frequency determining element, connections including two of saidV crystal electrodes connecting the oscillation generating electrodes ofI the other of said systems in a regenerative circuit including said crystal as a frequency determining element, there being reactance included between said crystal electrodes in said connections, means i for varying the reactance between the two crystal electrodes in at least one of saidk regenerative circuits and connections for differentiallymodulating said systems in accordance with signals.

6. A modulator as recited in claim 5 wherein said reactance comprises the capacity lbetween crystal electrodes and wherein adjustable mountings are provided for at least one of the crystal electrodes in said-one of said regenerative circuits y for varying said reactance.

7. A modulator as recited in claim 5 wherein said-reactance between the two crystal electrodes in at least one of said generating circuits comprises a. variable condenser.

8. In a wave length modulation system a pair of electron discharge tubes each having oscillation generating electrodes, a piezo-electric crystal in a three electrode crystal holder, connections including a pair of said crystal electrodes coupling the oscillation generating electrodes of one of said tubes in a regenerative circuit including said crystal, connections including one of said first pair of crystal electrodes and the remaining crystal electrode coupling the oscillation generating electrodes of the other tube in a regenerative circuit including said crystal, a tuning capacity shunting at least a pair of said crystal electrodes for tuning said crystal to operate at one frequency in one of said regenerative circuits and to operate at a different frequency in the other of said regenerative circuits, means in said circuits for entraining the same to operate at a third frequency, means for diiferentially modulating said tube impedances in accordance with signals and an output circuit coupled to said regenerative circuits.

9. In-a wave length modulation system a pair of electron discharge devices each having a control electrode and output electrodes including a cathode electrode, a piezo-electric crystal in a holder having three electrodes, a coupling between one of said crystal holder electrodes and the cathodes of said devices, a coupling between a second one of said crystal holder electrodes and the control electrode of one of said devices, a coupling between the third of said crystal holder electrodes and the control electrode of the other 'of said devices, a capacity shunting at least; the crystal holder electrode coupled to the cathodes of said devices and another of said crystal electrodes for tuning said crystal to operate at one frequency in one of said couplings and to operate at a second frequency in the other of said couplings, said crystal and couplings beingA entrained to operate at a third frequency, an output circuit coupled to said devices and means for modulating the impedances of said devices in phase displaced relation in accordance with signals.`

10. In a wave length modulation system a. pair oi' electron discharge devices each having oscillation generating electrodes including a cathode, a control electrode and an additional electrode serving as an anode, a'piezo-electric crystal having three electrodes, a coupling between one of said piezo-electric crystal electrodes and the cathodes of said devices, a coupling between a control electrode of the other of said devices and a second one of the crystal electrodes, a coupling between the control electrode of the other device and the third crystal electrode, a tuned output circuit coupled to electrodes of said devices, each of said devices being in a regenerative circuit including said crystal and operating to generate oscillations,

a variable capacity for tuning the pair of crystal rst and second frequencies, and means for dif` I ferentially modulating said devices in accordance with signals.

' MURRAY G. CROSBY. 

